The present invention relates to nebulizers for inhalation therapy. It more particularly concerns a nebulizer having improved moisturizing capability with a wider range of oxygen percentage and less susceptibility to variation of back pressure.
In common forms of inhalation therapy, oxygen or an oxygen enriched mixture of air is provided for introduction to a patient's lungs by means of suitable breathing apparatus. The gas mixture is preferably moisturized and transmitted to the patient through a flexible tube which may be several feet or more in length. Particularly where such a tube is corrugated, but even where it is not, water in the moisturized gas mixture tends to drop out of the mixture, collecting in lower portions or bends of the connecting conduit. The water collected in the conduit may increase in volume to a point where the connecting conduit is either partially or entirely blocked, thereby greatly endangering the patient by obstruction of the supply of breathable gas.
The nebulizer provides a gas stream that entrains water particles rather than water vapor (as in a humidifier). It requires a minimum water particle size because it must insure that water particles will reach deeper portions of the respiratory tract. In a humidifier the gas carries water vapor rather than water particles and the moisture in the inhaled mixture may be absorbed before it reaches deeper portions of the respiratory tract. In the nebulizer, liquid particle size preferably is from about five microns down to about two microns. Particles larger than five microns have a greatly increased tendency to drop out of the mixture during flow from the nebulizer to the patient. It is these large size particles that must be avoided. Thus, large particles in the mixture do no good to the patient because they generally do not remain in the mixture for time long enough to reach the patient. But more importantly, they tend to collect and fully or partially occlude the connecting tubing, requiring frequent attention and draining of the tubing to avoid complete blocking of flow.
Prior attempts to remove larger droplets from the inhalation mixture are basically ineffective, inefficient, complex, and costly. For example, the U.S. Pat. No. to Cronenberg, 4,243,396, describes a tortuous spiral path formed between a pair of telescoping tubes as a separator of gas droplets. The U.S. Pat. No. to Kienholz et al, 4,267,974, describes a chamber which is termed a baffling chamber having a baffle plate at the chamber exit. The U.S. Pat. No. to Schwartz et al, 4,177,945, shows a tortuous path that results in turbulent flow for removal of liquid droplets. These arrangements are largely ineffective, greatly complicating nebulizer structure, thereby increasing costs and compromising efficiency.
Prior nebulizers have other problems, such as limited range of oxygen content of the output mixture and sensitivity to back pressure, which derive from the nature of their use and operational structure.
A nebulizer is used to provide a gas mixture that may be selectively varied from a high oxygen content to as little as 28% oxygen. Thus, the nebulizer is often provided with an adjustable air intake through which selectively varying amounts of air are admitted to the mixing chamber for mixing with the pure oxygen that is supplied under pressure.
Because air is generally drawn into the mixing chamber of the nebulizer by venturi action of a high-velocity oxygen stream, which provides the low pressure for drawing the air in, the minimum amount of oxygen percentage in the outgoing mixture is limited. Air itself has an oxygen content of about 21%, and thus it is not possible, by the negative pressure of venturi action of a stream of pure oxygen, to draw in enough air to obtain an oxygen content in the output of the nebulizer below 28%, as is often required or desired. Many nebulizers are not capable of providing an outgoing mixture having an oxygen content of less than about 35%, and oxygen content of less than about 28% has been available previously only with expensive and complex additional regulating equipment.
Normally, a nebulizer is adjusted to provide a desired predetermined oxygen flow rate, such as, for example, in the order of about five liters per minute, to thereby provide a desired output flow rate of the moisturized oxygen-enriched inhalation mixture of 28% oxygen. However, back pressure of various devices, including the patient mask and hoses interconnected between the mask and the nebulizer, will cause variation of the air entrainment input flow rate from a desired value, which, in turn, causes variation in the percentage of oxygen in the output mixture. Thus, outputs of prior nebulizers have been difficult to precisely control. Still further, the large droplets of water which fall out in the tubing connecting the nebulizer with the patient are waste, in addition to providing undesirable collections of water in the tubing, and generally indicate an inefficiency of complete utilization of the sterile water that is used.
Accordingly, it is an object of the present invention to provide a nebulizer that avoids or minimizes above mentioned disadvantages.